Efficient Computation of Kubo Conductivity for Incommensurate 2D Heterostructures

TL;DR

This paper presents a new numerical method to efficiently compute the Kubo conductivity in incommensurate 2D heterostructures, especially effective at low frequencies and temperatures, demonstrated on twisted bilayer graphene.

Contribution

The paper introduces a momentum space formulation and algorithm for calculating conductivity in incommensurate 2D heterostructures within a tight-binding framework, improving efficiency.

Findings

Efficient conductivity computation at low frequencies and temperatures.

Applicable to a wide class of 2D materials.

Demonstrated on twisted bilayer graphene with small twist angles.

Abstract

Here we introduce a numerical method for computing conductivity via the Kubo Formula for incommensurate 2D bilayer heterostructures using a tight-binding framework. We begin with deriving the momentum space formulation and Kubo Formula from the real space tight-binding model using the appropriate Bloch transformation operator. We further discuss the resulting algorithm along with its convergence rate and computation cost in terms of parameters such as relaxation time and temperature. In particular, we show that for low frequencies, low temperature, and long relaxation times conductivity can be computed very efficiently using momentum space for a wide class of materials. We then demonstrate our method by computing conductivity for twisted bilayer graphene (tBLG) for small twist angles.